In a wheel loader, a power from an engine is provided to a traveling power train and a hydraulic pump; drive wheels are driven through the traveling power train; and work equipment and so on are operated through the hydraulic pump. In other words, output (torque) of the engine is transmitted to the drive wheels through the traveling power train (power transmission device) such as a torque converter and a transmission. With this configuration, the drive wheels are driven and the wheel loader is made travel. As described above, part of horsepower from the engine is consumed as torque converter absorption horsepower.
Additionally, the engine output is transmitted to the hydraulic pump to make the hydraulic pump drive. In the way stated above, pressurized oil is supplied from the hydraulic pump to a hydraulic actuator (hydraulic cylinder) to actuate work equipment (boom, bucket, etc.), a cooling fan and so on, and operations and so on are carried out. As described above, part of the horsepower from the engine is consumed as pump absorption horsepower.
As one mode of the operations carried out by the wheel loader, there exists a loading operation as shown in FIG. 1.
In other words, the wheel loader 100 excavates and scoops grounds, earth and sand and other loads by a bucket 90. After the load is scooped, the bucket 90 is put into a tilt end position (FIG. 1A). Then, the vehicle moves forward while lifting a boom (lift arm) 80 (FIGS. 1B and 1C). After that, the load in the bucket 90 is dumped and loaded to a dump body of a dump truck 200 (FIG. 1D).
Here, at the time of dump approach, when the wheel loader 100 moves forward while lifting the boom 80 and approaches the dump truck 200, a brake is actuated to stop at a place of the dump truck 200.
A wet disc brake unit is employed as a brake unit, and is provided to a front and a rear axles. Additionally, for the front and the rear axles, various types of gears and so on are provided, and are soaked into axle oil to lubricate sliding surfaces of the gears and so on.
Patent Literature 1 below provides an invention in which it is determined, by detecting a vertical position of a boom, whether or not it is in a dump approach; and, when it is determined that it is in the time of dump approach, an automatic transmission device is controlled so as not to shift down, whereby a state where a hard braking occurs due to the shift down can be avoided.    Patent Literature 1: Japanese Patent Application Laid-open No. 63-265730